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Engine temp dropped to 120F

90Pioneer

NAXJA Forum User
Location
USA
So last night I was out on a night run doing some wheeling in a local area. Granted, it was pretty f*cking cold (about 0 degrees), but my engine had been running at 180, maybe a touch warmer all night long. Has a new, dealer installed thermostat less than six months old. So we're driving and nothing really has changed in what I'm doing, but all the sudden the heater starts blowing luke warm air. I look at the engine temp gauge and it had gone down to below 120.

I figured the thermostat might had stuck open, dispite being new. I pulled over and beat on the thermostat housing with the cap end of a 20oz soda bottle. Continued driving about 1/2 mile so see if it would warm up any, but I could watch the gauge go down as I drove. So I stopped again and taped a bag over my grill to block as much air flow as I could. This seemed to work, and my engine ran at normal, or almost normal temps the rest of the way home.

Can the 4.0 just not produce enough heat to warm itself in sub freezing temps, or was my thermostat just stuck open for a little while?
 
Sounds like a stuck open thermostat to me. The fact that the motor warmed up after you restricted air flow to the radiator shows that the radiator was cooling the water too much. If the thermostat had been working properly, less water would have flowed thru the radiator, and the radiator wouldn't have been able to do so much cooling.
 
90Pioneer said:
Can the 4.0 just not produce enough heat to warm itself in sub freezing temps, or was my thermostat just stuck open for a little while?

The t'stat was stuck open so an abnormally large amount of coolant was able to flow through the radiator and lose heat. Peplace the t'stat with a Robertshaw 195* unit. It's much better than the OEM version.
 
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